1. Field of Invention
This invention relates to a gear pump for feeding an elastomeric material to a die providing components for building a tire. The gear pump of this invention is especially useful in minimizing the temperature differential across the face of the gears and avoiding pressure spikes experienced with herringbone gear teeth. The pumped material is also metered without causing pulsations such as those experienced during unloading a gear pump with spur gear teeth.
2. Description of the Related Art
Gear pumps such as those shown in U.S. Pat. No. 5,267,847 have been proposed for extruding strips of rubber for tire components wherein the gears are spur gears. The spur gears have caused the rubber to be ejected from the gear pump with pulsations corresponding to the pumping action of the axially oriented spaced gear teeth. This results in extruded components which are not uniform and do not meet the specifications for building tires.
It has also been proposed to use helical gears in a gear pump to reduce the pulsations. However, the elastomeric material is pushed to one side resulting in a product which is heavy on one side and with a higher temperature on one side than on the other side. This temperature differential is not desirable because the viscosity of the rubber will then be greater on one side resulting in a non-uniform extrusion of the component.
A no-backlash gearing mechanism such as that described in U.S. Pat. No. 5,636,550 has been proposed for eliminating backlash in a gear drive chain. Intermeshing gears having curved teeth have also been proposed for adjacent shafts in U.S. Pat. No. 5,533,825. However, there is no teaching or showing of utilizing curved gear teeth in a gear pump.
Gear pumps with gears having herringbone teeth are shown in U.S. Pat. No. 4,137,023. The teeth are joined at sharp central edges which cause high pressure spikes resulting in an increase in temperature of the elastomeric material at the central portions of the component which may produce a non-uniform component. Gear pumps for melted synthetic thermoplastic material are shown and described in U.S. Pat. No. 5,458,474 however, the gear teeth are herringbone shaped and have the sharp central edges which cause pressure spikes.